Lubricants used in high temperature environments must exhibit low evaporation such that effective lubrication is maintained for an extended period to ensure the proper functioning of the lubricated equipment and to prevent damage thereto. Lubricants that evaporate quickly require the apparatus to be more frequently lubricated to replace the evaporated lubricant. Furthermore, high temperature lubricants must exhibit low deposit formation as deposits can inhibit rather than facilitate movement of lubricated parts. However, many conventional lubricants oxidize when used at high temperatures, which causes the formation of hard, lacquer-like deposits. The formation of deposits negatively impacts movement of the lubricated surfaces and necessitates periodic cleaning to remove the deposits, which can be time-consuming and inconvenient. Maximizing one property of a lubricant often sacrifices performance in the other property, so the key for optimal lubricant performance is to achieve a formulation that has both low evaporation and minimal deposit formation.
The choice of base oil used in the lubricant composition plays an important role in determining the amount and type of deposit formation that will occur when the lubricant composition is used in high temperature applications. Various base oils are used to create lubricant compositions including but not limited to mineral oils, vegetable oils, synthetic hydrocarbons, polyol esters, synthetic esters, complex esters, polyglycols, alkylated aromatics, and silicones. Ester fluids, specifically synthetic esters, are particularly useful as high temperature lubricants. Esters are useful in high temperature applications because other base oils suffer from high evaporation, smoke, and formation of hard carbon deposits when used at high temperatures. While ester fluids generally perform well at high temperatures, certain types of ester fluids, such as complex esters, have a tendency to polymerize at high temperatures, resulting in the formation of hard deposits that do not readily evaporate. As a result, complex esters are generally not useful in lubricant compositions for use at high temperatures where low deposit formation is desired. As such, it is desirable to further improve upon the performance of ester base oils to effectively lubricate equipment that operates under extreme and demanding conditions.
In some applications, such as lubricating a conveyor chain driven by a motor, a thin film of lubricant is applied to the conveyor chain at a regular lubrication interval of roughly four to eight hours. However, conventional high temperature lubricants may evaporate relatively quickly, resulting in a shorter lubrication interval. Furthermore, conventional high temperature lubricants have a tendency to polymerize and form hard deposits that must be manually removed, by scraping or otherwise. The hard deposits inhibit movement of the lubricated parts causing premature wear, sticking, and breakage. As the lubricant evaporates and forms deposits, the motor used to drive the conveyor chain must work harder and use more energy. This results in more frequent maintenance of the apparatus, and requires that the conveyor chain be manually cleaned via scraping or the like.
Thus, there exists a need in the art for a high temperature lubricant that has low evaporation to allow for a longer lubrication interval and low deposit formation. More specifically, there exists a need in the art for a lubricant composition that may be used in high temperature application that forms only soft deposits, if any, so as to minimize the need for cleaning and maintenance of the lubricated apparatus.